Thanks for your post. It seems unusual that a charge for $0 would get an ‘insufficient funds’ error message but the example provided in the conversation with Support that you mentioned was too long ago for us to be able to investigate for more details.
If you have a more recent example from within the past 7 days we recommend submitting a new report through the ‘Email’ option in the [Partner Support Contact] menu using the ‘App Development & API’ category to enable a deeper investigation into the issue. Thank you.